Add early-out for topmost node

source

@@ -108142,10 +108142,12 @@ document.body.appendChild(text);
 
      <li><p><span>Reset the insertion mode appropriately</span>.</p></li>
 
-     <li><p>If the start tag for the <span data-x="concept-declarative-template-element">declarative template element</span> had an attribute with the name "shadowroot" whose value was an ASCII case-insensitive match for the strings "open" or "closed", then mark the template element as a
-     <dfn><var data-x="concept-declarative-shadow-root">"declarative shadow root"</var></dfn>. Let the <dfn><var data-x="concept-declarative-shadow-mode">declarative shadow mode</var></dfn> be the value of the "shadowroot" attribute.</p></li>
+     <li><p>If the start tag for the <span data-x="concept-declarative-template-element">declarative template element</span> did not have an attribute with the name "shadowroot" whose value was an ASCII case-insensitive match for the strings "open" or "closed", then stop this algorithm.</p></li>
 
-     <li><p>If the template element is not a <span data-x="concept-declarative-shadow-root">declarative shadow root</span>, then stop this algorithm.</p></li>
+     <li><p>If the <span>adjusted current node</span> is the topmost element in the <span>stack of open elements</span>, then stop this algorithm.</p></li>
+
+     <li><p>Let the <dfn><var data-x="concept-declarative-shadow-mode">declarative shadow mode</var></dfn> be the value of the
+     <span data-x="concept-declarative-template-element">declarative template element</span>'s start tag's "shadowroot" attribute.</p></li>
 
      <li><p>If the start tag for the <span data-x="concept-declarative-template-element">declarative template element</span> had an attribute with the name "shadowrootdelegatesfocus", then let <dfn><var data-x="concept-declarative-shadow-delegates-focus">declarative shadow delegates focus</var></dfn> be true. Otherwise let it be false.</p></li>